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The dew point is the temperature the air needs to be cooled to (at constant pressure) in order to produce a relative humidity of 100% [1].This temperature depends on the pressure and water content of the air.
Dew point temperature (DPT) is the temperature at which a moist air sample at the same pressure would reach water vapor "saturation." At this point further removal of heat would result in water vapor condensing into liquid water fog or, if below freezing point, solid hoarfrost. The dew point temperature is measured easily and provides useful ...
Atmospheric pollutant concentrations expressed as mass per unit volume of atmospheric air (e.g., mg/m 3, μg/m 3, etc.) at sea level will decrease with increasing altitude because the atmospheric pressure decreases with increasing altitude. The change of atmospheric pressure with altitude can be obtained from this equation: [2]
is dew point temperature at pressure , e {\displaystyle e} is the water vapor pressure (to obtain θ L {\displaystyle \theta _{L}} for dry air), κ d = R d / c p d {\displaystyle \kappa _{d}=R_{d}/c_{pd}} is the ratio of the specific gas constant to the specific heat of dry air at constant pressure (0.2854),
His equation makes use of the relationship between the LCL and dew point temperature discussed above. In the Earth's atmosphere near the surface, the lapse rate for dry adiabatic lifting is about 9.8 K/km, and the lapse rate of the dew point is about 1.8 K/km (it varies from about 1.6-1.9 K/km). This gives the slopes of the curves shown in the ...
It is necessary to measure temperatures of both the condensation and evaporation, because the dew point is the equilibrium temperature at which water both condense and evaporate at the same rate. When cooling the mirror, the temperature keeps dropping after it has reached the dew point thus, the condensation temperature measurement is lower ...
A gravimetric hygrometer extracts the water from the air (or other gas) and weighs it separately, for example by weighing a desiccant before and after it has absorbed the water. The temperature, pressure and volume of the resulting dry gas are also measured, providing enough information to calculate the amount of water per mole of gas. [8] [9]
It is used by industrial hygienists, athletes, sporting events and the military to determine appropriate exposure levels to high temperatures. A WBGT meter combines three sensors, a dry-bulb thermometer, a natural (static) wet-bulb thermometer, and a black globe thermometer. [2]